Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare read-only and idempotent, so safety is covered. The description adds valuable behavioral context: it returns 'regular' when the market is open, and it focuses on off-hours session data. This goes beyond the annotation hints.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two concise sentences, front-loaded with the main purpose ('Live view of the current off-hours session') and includes necessary detail about the return value condition. No unnecessary words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple zero-parameter tool with no output schema, the description is complete. It tells the user what data is shown (tickers with largest premium/discount) and the behavior during market open ('regular'). No significant gaps.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool has zero parameters, so the baseline is 4. The description doesn't need to explain parameter semantics, and it doesn't. Schema coverage is 100% by default since there are no properties.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's function: 'Live view of the current off-hours session' showing tickers with largest premium/discount vs last close. It distinguishes itself from siblings like hood_gap_sessions (likely historical) and hood_gaps_summary (likely summary) by emphasizing 'live' and 'current'.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It provides clear context: this is for the current off-hours session, and when the market is open it returns 'regular'. This implies it should be used only during off-hours for live gap data. It doesn't explicitly name alternatives but the context is sufficient to differentiate from sibling tools.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.